Apparatus and method for optimized route invalidation using modified no-path dao signaling

ABSTRACT

Apparatus and method for optimized route invalidation using modified no-path DAO signaling are disclosed. According to the present invention, a node switching its current parent is adapted to send a regular Destination Oriented Directed Acyclic Graph (DODAG) Advertisement Object (DAO) message. Using the changed signaling, the common ancestor node generates an NPDAO on behalf of the switching node on receiving a refreshed DAO from an alternate path. The common ancestor node according to the present invention reuses a same PathSequence from the regular DAO based on which the NPDAO gets generated. The common ancestor node detects routing anomaly using next hop mismatch on reception of the DAO to generate the NPDAO on behalf of the target node. The No-Path DAO traverses downward/downstream along the previous path, unlike any other DAO messages traverses upstream according to convention approaches. The present invention provides a new signaling mechanism for route invalidation in constrained networks.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of International Application No.PCT/CN2017/105886, filed on Oct. 12, 2017, which claims priority toIndia Patent IN201641043305, filed on Dec. 19, 2016. The disclosures ofthe aforementioned applications are hereby incorporated by reference intheir entireties.

TECHNICAL FIELD

The present subject matter described herein, in general, relates torouting of packets in communication networks and more particularly tooptimizing route invalidation using modified No-Path DAO signaling.

BACKGROUND

Internet of Things (IoT) enables all the general purposedevices/appliances, sensors/actuators available in the network to beconnected to the Internet, thus allowing a greater control in terms ofmonitoring, commanding these devices from anywhere and anytime. Anexample to be given is Building Automation where all the sensors (firesensors, temperature sensors, etc), lights, room curtains, door locks,are connected to the Internet and can be controlled remotely/locallyusing a mobile application or any other easy-to-use device.

Low-Power and Lossy Networks (LLN) is a network of spatially distributedautonomous and resource constrained sensors/actuators to monitorphysical or environmental conditions, such as temperature, sound,pressure, etc and to cooperatively pass their data through the networkto a main location. The nodes in such a network are extremely resourceconstrained and the network is usually bandwidth constrained. Generally,the networks are constructed in a mesh formation such that nodes connectto one or more than one intermediate routers to reach border router. Arouting protocol is responsible for identifying optimum pathsdynamically, switch paths in case of failures and establish P2P, P2MP,MP2P traffic paths. The protocols are tailored and in some casesredesigned to suit such node/network characteristics. For e.g. a routingprotocol such as open shortest path first (OSPF) which is usually wellsuited for regular non-constrained networks will fail miserably in LLNsbecause of lossy and constrained nature of the network. Thus a differentrouting protocol (such as Routing Protocol for LLNs (RPL)) is used inLLNs which are relatively less aggressive to link/path failures i.e.they do not over-react to failures resulting in reduced controloverhead.

An exemplary network subsystem is as shown in FIG. 1. The devices asshown in FIG. 1 usually form a network in an ad-hoc mode wherein devicesconnect to each other to eventually reach a Border Router (BR) throughwhich the devices are connected to the Internet.

As discussed in RFC6550, RPL specifies a proactive (i.e. paths areformulated before the data exchange begins) distance-vector basedrouting scheme. Destination Oriented Directed Acyclic Graph (DODAG)Information Object (DIO) messages are percolated downstream to establishupstream paths. For downstream paths, the specification has an optionalmessaging in the form of DODAG Advertisement Object (DAO) messages usingwhich the 6LBR can learn route towards any of the nodes. In storingmode, DAO messages would result in routing entries been created on allintermediate hops from the node's parent all the way towards the 6LBR.

RPL allows use of No-Path DAO (NPDAO) messaging to invalidate a routingpath (the process of route deletion is also called route invalidation)and thus releasing of any resources utilized on that path. An NPDAO is aDAO message with route lifetime of zero, signaling route invalidationfor the given target. All the DAO messages are always sent upstream inthe network as per the current specification. RPL introduced NPDAOmessaging in the storing mode so that the node switching its currentparent can inform its parents and ancestors to invalidate the existingroute. Subsequently parents or ancestors would release any resources(such as the routing entry) it maintains on behalf of that child node.The NPDAO message always traverses the RPL tree in upward direction,originating at the target node itself.

For example, FIG. 2 illustrates a network topology implementing DAO andNPDAO signalling. As shown in FIG. 2, Node (D) is connected viapreferred parent (B). (D) have an alternate path via (C) towards the BR.Node (A) is the common ancestor for (D) for paths through (B)-(G) and(C)-(H). When (D) switches from (B) to (C), RPL suggests sending No-PathDAO to (B) and regular DAO to (C). The NPDAO via (B) should clearrouting states along the path (B)->(G)->(A)->(BR). A subsequent DAO from(D) via (C) should create new routing path via (C)->(H)->(A)->(BR).

Nodes in LLNs are generally resource constrained. There is limitedmemory available and routing entry records are the one of the primaryelements occupying dynamic memory in the nodes. Route invalidation helpsthe router nodes to decide which entries could be discarded to betterachieve resource utilization in case of contention. Thus it becomesnecessary to have an efficient route invalidation mechanism. Further, itis observed that a single parent switch may result in a “sub-tree”switching from one parent to another. Thus the route invalidation needsto be done on behalf of the sub-tree and not the switching node alone.Referring again to FIG. 2, when Node (D) switches parent, the routeinvalidation needs to be done for (D), (E) and (F). Thus withoutefficient route invalidation, a router may have to hold a lot ofunwanted route entries.

As per technical observations, a person skilled in the art understandsthat a node switches the parent and may employ No-Path DAO messagingwhen:

-   -   Current parent becomes unavailable because of transient or        permanent link or parent node failure.    -   The node finds a better parent node i.e. the metrics of another        parent is better than its current parent.    -   The node switches to a new parent whom it “thinks” has a better        metric but does not in reality.

The usual steps of operation when the node switches the parent is thatthe node sends a NPDAO message via its current parent to invalidate itscurrent route and subsequently it tries to establish a new routing pathby sending a new DAO via the new parent.

However, the existing mechanisms providing the NPDAO have certainlimitations and hence disadvantages, some of the technical drawbacks areas discussed below:

Lost NP-DAO due to Link break to the previous parent: When the nodeswitches the parent, the NPDAO is to be sent via the previous parent anda regular DAO via its new parent. In cases where the node switches theparent because of transient or permanent parent link/node failure thenthe NPDAO message is bound to fail. RFC6550 assumes communication linkwith the previous parent for NPDAO messaging. Further RFC6550 mentionsuse of route lifetime to remove unwanted routes in case the routes couldnot be refreshed. But route lifetimes in case of LLNs could besubstantially high and thus the route entries would be stuck for long.

Invalidate routes to dependent nodes of the switching node: NPDAO issent by the node who has switched the parent but it does not work forthe dependent child nodes below it. RFC6550 does not specify how routeinvalidation will work for sub-child's resulting in stale routingentries on behalf of the sub-child's on the previous route. The only wayfor a router to invalidate the route entries for dependent nodes wouldbe to use route lifetime expiry which could be substantially high forLLNs. Thus, for network topology as shown ion FIG. 2, when Node (D)switches its parent, Node (D) generates an NPDAO on its behalf. Postswitching, Node (D) transmits a DIO with incremented DTSN so that childnodes, node (E) and (F), generate DAOs to trigger route update on thenew path for themselves. There is no NPDAO generated by these childnodes through the previous path resulting in stale entries on nodes (B)and (G) for nodes (E) and (F).

Route downtime caused by asynchronous operation of NPDAO and DAO: Aswitching node may generate both an NPDAO and DAO via two differentpaths at almost the same time. There is a possibility that an NPDAOgenerated may invalidate the previous route and the regular DAO sent viathe new path gets lost on the way. This may result in route downtimethus impacting downward traffic for the switching node. Thus, fornetwork topology as shown ion FIG. 2, consider Node (D) switches fromparent (B) to (C) because the metrics of the path via (C) are better.Note that the previous path via (B) may still be available (albeit atrelatively bad metrics). An NPDAO sent from previous route mayinvalidate the existing route whereas there is no way to determinewhether the new DAO has successfully updated the route entries on thenew path. An implementation technique to avoid this problem is tofurther delay the route invalidation by a fixed time interval afterreceiving an NPDAO, considering the time taken for the new path to beestablished. Coming up with such a time interval is tricky since the newroute may also not be available and it may subsequently require moreparent switches to establish a new path.

Impact on P2P traffic: The P2P traffic in the previous sub-DODAG will beimpacted because the route entries in the sub-DODAG are stale and doesnot reflect the latest state of network information. Referring now toFIG. 3, a network topology showing problems associated with the NPDAOmessaging is shown. As shown in FIG. 3, NPDAO takes a path which thetarget decides not to use. The dependent nodes (E) and (F) nevergenerate NPDAO, and thus there is no route invalidation for them. Theimpact of this is that the NPDAO and DAP takes different paths and areasynchronous. In P2P traffic, when node (J) sends a communication packetto (E), (G) will try to route through (B) and it will fail.

In order to solve the issues associated with the existing mechanismsproviding the NPDAO, the prior-art provides certain solution as providedbelow:

NPDAO can be generated by the parent node who detects link failure tothe child: According to RFC6550, RPL states mechanisms which could beutilized to clear DAO states in a sub-DODAG. Section 11.2.2.3 of theRFC6550 states with DAO inconsistency loop recovery, a packet can beused to recursively explore and clean up the obsolete DAO states along asub-DODAG. Thus in the sample topology in FIG. 2, when Node (B) detectslink failure to (D), (B) has an option of generating an NP-DAO on behalfof Node (D) and its sub-child's, (E) and (F).

NP-DAO can be generated once the link is restored to the previousparent: This solution solves a specific scenario of transient links. Thechild node can detect that the connection to previous parent is restoredand then transmit an NP-DAO to the previous parent to invalidate theroute. This scheme is stateful, thus requires more memory and solves aspecific scenario.

Thus it may be noted form the above that, the technical problemsassociated with the solutions mentioned is that they cater to specificscenarios such as transient links. Further, there are problemsassociated with asynchronous generation of NPDAO from two differentnodes for the same target.

In detail, the DAO state information in the form of path sequence playsa major role. Every target is associated with a path sequence numberwhich relates to the latest state of the target. The Section 7.1 of theRFC6550 explains the semantics of path sequence number. According to it,the target node increments the path sequence number every time itgenerates a new DAO. The router nodes en-route utilizes this pathsequence number to decide the freshness of target information. If anon-target node has to generate an NP-DAO then it could use followingtwo possibilities with Path Sequence number: Let the Path Sequencenumber of old regular DAO that flowed through (B) be x. The subsequentregular DAO generated by Node (D) will have sequence number x+1.

-   -   i. Node (B) uses the previous Path Sequence number from the        regular DAO i.e. NP-DAO (pathseq<=x) as shown in FIG. 4        (leftmost).    -   ii. Node (B) increments the Path Sequence number i.e. NP-DAO        (pathseq>x such as x+1, x+2) as shown in FIG. 4 (rightmost).

In case i, the NP-DAO (pathseq<=x) will be dropped by all theintermediate nodes since the semantics of Path Sequence number dictatesthat any DAO with an older Path Sequence number be dropped.

In case ii, there is a risk that the NP-DAO (pathseq>x) traverses up theDODAG and invalidates all the routes till the root and then the regularDAO (pathseq>x) from the target traverses upwards. In this case theregular DAO (pathseq>x) will be dropped from common ancestor node to theroot. This will result in route downtime.

Another problem with this scheme is its dependence on the upstreamneighbor to detect that the downstream neighbor is unavailable. Thereare two possibilities by which such detection might be put to work:

-   -   i. There is P2P traffic from the previous sub-DODAG to any of        nodes in the sub-tree which has switched the path. In the above        example, let's consider that Node (G) has P2P traffic for either        of nodes (D), (E), or (F). In this case, Node (B) will detect        forwarding error while forwarding the packets from Node (B) to        (D). But dependence on P2P traffic may not be an optimal way to        solve this problem considering the reactive approach of the        scheme. The P2P traffic pattern might be sparse and thus such        detection might kick-in too late.    -   ii. The other case is where Node (B) explicitly employs some        mechanism to probe directly attached downstream child nodes.        Such kinds of schemes are seldom used.    -   iii. In case of sleepy nodes, RPL messaging cannot depend on any        such mechanisms described above.

Therefore, it is desirable to provide a mechanism that not only solvesthe above recited technical problems but also achieves efficient routeinvalidation, higher probability of NPDAO messaging success, less staleroutes, and reduced control overhead. It is also desirable to provide amechanism that enables routing tables in nodes to reflect latest stateof network.

The above-described deficiencies of existing mechanisms for NPDAOmessaging are merely intended to provide an overview of some of theproblems of conventional systems/mechanism/techniques, and are notintended to be exhaustive. Other problems with conventionalsystems/mechanism/techniques and corresponding benefits of the variousnon-limiting embodiments described herein may become further apparentupon review of the following description.

SUMMARY

This summary is provided to introduce concepts related to optimizingroute invalidation using modified No-Path DAO signaling, and the sameare further described below in the detailed description. This summary isnot intended to identify essential features of the claimed subjectmatter nor is it intended for use in determining or limiting the scopeof the claimed subject matter.

The object of the present application is to provide apparatus and methodfor optimized route invalidation using modified no-path DAO signaling.

According to a first aspect, a method for invalidating a routing path onswitching of a parent node. The method includes determining, by at leastone common ancestor node of a network, switching of the parent nodeassociated with at least one node based on at least one update messagereceived from the at least one node using a new routing path establishedon switching of the parent node; and generating, by the at least onecommon ancestor node, at least one No-Path message for invalidating therouting path associated with the at least one node on switching of theparent node.

When using the method according to the first aspect, the method achievesefficient route invalidation, higher probability of NPDAO messagingsuccess, less stale routes, and reduced control overhead, and enablesrouting tables in nodes to reflect latest state of network.

According to the first aspect, in a first possible implementation mannerof the first aspect, the method further comprises representing thenetwork by a Destination Oriented Directed Acyclic Graph (DODAG),wherein nodes in the graph represent at least the parent node, thecommon ancestor node, or the node, and the common ancestor node is aroot nodes root in the DODAG, and directed edges represent the linksbetween the node, wherein the at least one common ancestor node of thenetwork is a node having at least two nodes as descendants (the parentnode and/or the nodes) in the DODAG.

According to the first aspect or the above possible implementationmanners of the first aspect, in a second possible implementation mannerof the first aspect, wherein the routing path associated with the atleast one node is a path established for communication before switchingof the parent node.

According to the first aspect or the above possible implementationmanners of the first aspect, in a third possible implementation mannerof the first aspect, wherein the at least one update message is receivedfrom the at least one node while establishing new paths in the networkupon switching of the parent node.

According to the first aspect or the above possible implementationmanners of the first aspect, in a fourth possible implementation mannerof the first aspect, wherein the at least one node and the at least onecommon ancestor node are communicably coupled.

According to the first aspect or the above possible implementationmanners of the first aspect, in a fifth possible implementation mannerof the first aspect, wherein the at least one update message is adestination oriented directed acyclic graph advertisement object (DAO)message.

According to the first aspect or the above possible implementationmanners of the first aspect, in a sixth possible implementation mannerof the first aspect, wherein the at least one No-Path message is aNo-Path destination oriented directed acyclic graph advertisement objectmessage (NPDAO) message.

According to the first aspect or the above possible implementationmanners of the first aspect, in a seventh possible implementation mannerof the first aspect, wherein the at least one common ancestor nodedetermines switching of the parent node associated with the at least onenode for generating the at least one No-Path message by detecting thatthe at least one update message received from the at least one node isdifferent from the at least one update message received earlier.

According to the first aspect or the above possible implementationmanners of the first aspect, in a eighth possible implementation mannerof the first aspect, wherein the at least one common ancestor nodedetermines switching of the parent node associated with the at least onenode for generating the at least one No-Path message by utilizing a PathSequence form the at least one update message received. The at least onecommon ancestor node comprises a pre-stored Path sequence associated theat least one node before switching of the path, when the at least oneupdate message received, the Path sequence form the at least one updatemessage received is compared with the pre-stored path sequenceassociated the at least one node, and thereby generating the at leastone No-Path message.

According to the first aspect or the above possible implementationmanners of the first aspect, in a ninth possible implementation mannerof the first aspect, wherein the at least one update message receivedfrom the at least one node comprises at least one bit, representinginvalidating the routing path, placed in at least a target container orat least a transit information container or any combination thereof, theat least one bit authorizing generation of the at least one No-Pathmessage by the at least one common ancestor node.

According to the first aspect or the above possible implementationmanners of the first aspect, in a tenth possible implementation mannerof the first aspect, wherein the at least one No-Path message generatedcomprises at least one bit, representing reverse flag, adapted totraverse the No-Path message downstream/reverse, and placed in a basemessage level of the No-Path message.

According to the second aspect, a method for invalidating a routing pathon switching of a parent node in a network, wherein the network isrepresented by a Destination Oriented Directed Acyclic Graph (DODAG),the nodes in the graph represent at least the parent node, at least acommon ancestor node, or at least a node, and the common ancestor nodeis a root nodes root in the DODAG, and directed edges represent thelinks between the node for routing packets between the nodes. The methodincludes: determining, by the at least one common ancestor node of thenetwork, switching of the parent node associated with the at least onenode based on at least one a destination oriented directed acyclic graphadvertisement object (DAO) message received from the at least one nodeusing a new routing path established on switching of the parent node;and generating, by the at least one common ancestor node, at least oneNo-Path destination oriented directed acyclic graph advertisement objectmessage (NPDAO) message for invalidating the routing path associatedwith the at least one node on switching of the parent node.

According to the second aspect, in a first possible implementationmanner of the second aspect, wherein the routing uses a Routing Protocolfor Low Power and Lossy Networks (RPL).

According to the second aspect or the above possible implementationmanners of the second aspect, in a second possible implementation mannerof the second aspect, further includes receiving, by the at least onecommon ancestor node of the network, the DAO message from the at leastone node; determining a mismatch in a next hop of a routing entryassociated with a Path sequence pre-stored against a next hop of arouting entry associated with a Path sequence of the DAO messagereceived; and thereby generating, by the at least one common ancestornode, the at least one No-Path destination oriented directed acyclicgraph advertisement object message (NPDAO) message for invalidating therouting path associated with the at least one node on switching of theparent node.

According to the second aspect or the above possible implementationmanners of the second aspect, in a third possible implementation mannerof the second aspect, wherein the NPDAO message traversesdownward/downstream along the Path sequence of the DAO message received.

According to the second aspect or the above possible implementationmanners of the second aspect, in a fourth possible implementation mannerof the second aspect, wherein the at least one DAO message is generatedby the at least one node to establish new paths on switching of theparent node.

According to the second aspect or the above possible implementationmanners of the second aspect, in a fifth possible implementation mannerof the second aspect, further includes utilizing the Path sequence fromthe at least one DAO message to generate the NPDAO message.

According to the second aspect or the above possible implementationmanners of the second aspect, in a sixth possible implementation mannerof the second aspect, wherein the at least one update message receivedfrom the at least one node comprises at least one bit, representinginvalidating the routing path, placed in at least a target container orat least a transit information container or any combination thereof, theat least one bit authorizing generation of the at least one No-Pathmessage by the at least one common ancestor node.

According to the second aspect or the above possible implementationmanners of the second aspect, in a seventh possible implementationmanner of the second aspect, the at least one No-Path message generatedcomprises at least one bit, representing reverse flag, adapted totraverse the No-Path message downstream/reverse, and placed in a basemessage level of the No-Path message.

According to the third aspect, an apparatus for invalidating a routingpath on switching of a parent node is provided. The apparatus includes aprocessor, and a memory coupled to the processor for executing aplurality of modules present in the memory. The plurality of modulesincludes a determining module, and a generating module. The determiningmodule adapted to determine switching of the parent node associated withat least one node based on at least one update message received from theat least one node using a new routing path established on switching ofthe parent node. The generating module adapted to generate at least oneNo-Path message for invalidating the routing path associated with the atleast one node on switching of the parent node. Further, the modules,when executed by the processor, cause the processor to perform themethod of the first aspect or any one of the possible implementationmanners of the first aspect.

According to the fourth aspect, an apparatus for invalidating a routingpath on switching of a parent node in a network, wherein the network isrepresented by a Destination Oriented Directed Acyclic Graph (DODAG),the nodes in the graph represent at least the parent node, at least acommon ancestor node, or at least a node, and the common ancestor nodeis a root nodes root in the DODAG, and directed edges represent thelinks between the node for routing packets between the nodes isdisclosed. The apparatus includes a processor, and a memory coupled tothe processor for executing a plurality of modules present in thememory. The plurality of modules includes a determining module, and agenerating module. The determining module adapted to determine switchingof the parent node associated with the at least one node based on atleast one a destination oriented directed acyclic graph advertisementobject (DAO) message received from the at least one node using a newrouting path established on switching of the parent node. The generatingmodule adapted to generate at least one No-Path destination orienteddirected acyclic graph advertisement object message (NPDAO) message forinvalidating the routing path associated with the at least one node onswitching of the parent node. Further, the modules, when executed by theprocessor, cause the processor to perform the method of the secondaspect or any one of the possible implementation manners of the secondaspect.

According to the fifth aspect, a computer readable storage medium isprovided. The computer readable storage medium stores program codes. Theprogram codes comprise instructions for performing the method of thefirst aspect or any one of the possible implementation manners of thefirst aspect.

According to the fifth aspect, a computer readable storage medium isprovided. The computer readable storage medium stores program codes. Theprogram codes comprise instructions for performing the method of thesecond aspect or any one of the possible implementation manners of thesecond aspect.

In contrast to the available techniques, the present invention providesan apparatus and method for signaling NPDAO messaging whichsignificantly improves the route invalidation efficiency.

Further, the present invention also has technical advantages withrespect to the prior-art, some of the advantages are disclosed below:

-   -   i. Efficient route invalidation: The present invention improves        the route invalidation by ensuring that the NPDAO signaling        happens over an established path.    -   ii. Higher probability of NPDAO messaging success: Since the        signaling according to the present invention happens over an        established path, thus there is higher probability of messaging        success.    -   iii. Less stale routes: Because of optimal NPDAO messaging        according to the present invention, there is less probability of        stale routes on the intermediate routers. Thus in case of        contention, the node will have better control over which route        entries to be evicted.    -   iv. Routing tables in nodes will reflect latest state of        network: Because of optimized messaging according to the present        invention the routing table will have less stale entries and        thus reflect latest state of network topology.    -   v. Reduced Control Overhead: The present invention enables NPDAO        messaging to happen over only a subset of impacted nodes, thus        significantly reducing NPDAO control overhead. In earlier case        the NPDAO messaging took place between the switching nodes to        all the way till the border router.

Further, in contrast to the existing mechanisms, the present inventionprovides a way of signaling NPDAO by using a common ancestor node togenerate NPDAO rather than the target/switching node itself. Using thechanged signaling, the common ancestor node generates an NPDAO on behalfof the target node on receiving a refreshed/updated DAO from analternate path.

The present invention expects the switching node to send only theregular DAO (which is a conventional procedure for forming a network).In contrast to the existing mechanisms a common ancestor receives a DAOfor a target and finds a mismatch in next hop. The mismatch is detectedin the next hop in routing entry versus the next hop from which DAO isreceived. Thus, the common ancestor node is in charge of generating aNo-Path DAO on behalf of the switching node.

According to the current RPL specification RFC6550, the DAO messagealways traverses upstream, thus according to the present invention incontrast to the existing mechanisms and RFC6550, the NPDAO traversesdownward/downstream along the previous path, unlike any other DAO.

The various options and preferred embodiments referred to above inrelation to the first implementation are also applicable in relation tothe other implementations.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS

The detailed description is described with reference to the accompanyingfigures. In the figures, the left-most digit(s) of a reference numberidentifies the figure in which the reference number first appears. Thesame numbers are used throughout the drawings to refer like features andcomponents.

FIG. 1 illustrates an exemplary network subsystem.

FIG. 2 illustrates a network topology implementing the DAO and NPDAO.

FIG. 3 illustrates a network topology showing problems associated withthe current NPDAO messaging.

FIG. 4 illustrates an impact of path sequence state on async NPDAOgeneration.

FIG. 5 illustrates a network implementation having a common ancestor.

FIG. 6 illustrates a NPDAO signaling, in accordance with an embodimentof the present subject matter.

FIG. 7 illustrates a DAO processing according to the prior-art.

FIG. 8 illustrates DAO processing, in accordance with an embodiment ofthe present subject matter.

FIG. 9 (a) illustrates a conventional DAO object.

FIG. 9 (b) illustrates new flags required in DAO base object and Transitinformation container, in accordance with an embodiment of the presentsubject matter.

FIG. 10 illustrates working/use of new flags in DAO base object, inaccordance with an embodiment of the present subject matter.

FIG. 11 illustrates an apparatus for invalidating a routing path onswitching of a parent node in a network, in accordance with anembodiment of the present subject matter.

FIG. 12 illustrates a method for invalidating a routing path onswitching of a parent node in a network, in accordance with anembodiment of the present subject matter.

It is to be understood that the attached drawings are for purposes ofillustrating the concepts of the invention and may not be to scale.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

The following clearly describes the technical solutions in theembodiments of the present invention with reference to the accompanyingdrawings in the embodiments of the present invention. Apparently, thedescribed embodiments are merely a part rather than all of theembodiments of the present invention. All other embodiments obtained bya person of ordinary skill in the art based on the embodiments of thepresent invention without creative efforts shall fall within theprotection scope of the present invention.

The invention can be implemented in numerous ways, as a process, anapparatus, a system, a composition of matter, a computer readable mediumsuch as a computer readable storage medium or a computer network whereinprogram instructions are sent over optical or electronic communicationlinks. In this specification, these implementations, or any other formthat the invention may take, may be referred to as techniques. Ingeneral, the order of the steps of disclosed processes may be alteredwithin the scope of the invention.

A detailed description of one or more embodiments of the invention isprovided below along with accompanying figures that illustrate theprinciples of the invention. The invention is described in connectionwith such embodiments, but the invention is not limited to anyembodiment. The scope of the invention is limited only by the claims andthe invention encompasses numerous alternatives, modifications andequivalents. Numerous specific details are set forth in the followingdescription in order to provide a thorough understanding of theinvention. These details are provided for the purpose of example and theinvention may be practiced according to the claims without some or allof these specific details. For the purpose of clarity, technicalmaterial that is known in the technical fields related to the inventionhas not been described in detail so that the invention is notunnecessarily obscured.

In the following detailed description, numerous specific details are setforth in order to provide a thorough understanding of the invention.However, it will be understood by those skilled in the art that thepresent invention may be practiced without these specific details. Inother instances, well-known methods, procedures, and components,modules, units and/or circuits have not been described in detail so asnot to obscure the invention.

Although embodiments of the invention are not limited in this regard,discussions utilizing terms such as, for example, “processing,”“computing,” “calculating,” “determining,” “establishing”, “analyzing”,“checking”, or the like, may refer to operation(s) and/or process(es) ofa computer, a computing platform, a computing system, or otherelectronic computing device, that manipulates and/or transforms datarepresented as physical (e.g., electronic) quantities within thecomputer's registers and/or memories into other data similarlyrepresented as physical quantities within the computer's registersand/or memories or other information non-transitory storage medium thatmay store instructions to perform operations and/or processes.

Although embodiments of the invention are not limited in this regard,the terms “plurality” and “a plurality” as used herein may include, forexample, “multiple” or “two or more”. The terms “plurality” or “aplurality” may be used throughout the specification to describe two ormore components, devices, elements, units, parameters, or the like.Unless explicitly stated, the method embodiments described herein arenot constrained to a particular order or sequence. Additionally, some ofthe described method embodiments or elements thereof can occur or beperformed simultaneously, at the same point in time, or concurrently.

Apparatus and method for optimized route invalidation using modifiedno-path DAO signaling are disclosed.

While aspects are described for Apparatus and method for optimized routeinvalidation using modified no-path DAO signaling, the present inventionmay be implemented in any number of different computing systems,environments, and/or configurations, the embodiments are described inthe context of the following exemplary systems, devices/nodes/apparatus,and methods.

Henceforth, embodiments of the present disclosure are explained with thehelp of exemplary diagrams and one or more examples. However, suchexemplary diagrams and examples are provided for the illustrationpurpose for better understanding of the present disclosure and shouldnot be construed as limitation on scope of the present disclosure.

The present invention provides a way of signaling NPDAO by using commonancestor node to generate NPDAO rather than the target node itself.Using the changed signaling, the common ancestor node generates an NPDAOon behalf of the target node on receiving a refreshed DAO from analternate path.

Referring now to FIG. 5, a network topology is shown. As shown in FIG.5, node (A) is a common ancestor node of node (D). In graph theory andcomputer science, the lowest common ancestor (LCA) of two nodes v and win a tree or directed acyclic graph (DAG) T is the lowest (i.e. deepest)node that has both v and w as descendants, where we define each node tobe a descendant of itself (so if v has a direct connection from w, w isthe lowest common ancestor).

Thus, according to the present invention, using the changed signaling,the common ancestor node (node A in this case) generates an NPDAO onbehalf of the target node on receiving a refreshed DAO from an alternatepat

According to the present invention, a switching node (node whichswitches the parent) sends the regular DAO to a common ancestor node.The common ancestor node is in charge of generating a No-Path DAO(NPDAO) on behalf of the switching node.

The common ancestor receives the DAO from the switching node and finds amismatch in next hop. Mismatch is detected in the next hop in routingentry versus the next hop from which DAO is received.

The NPDAO traverses downward/downstream along the previous path, unlikeany other DAO (note that in current RPL specification, the DAO messagealways traverses upstream).

Referring now to FIG. 6, an NPDAO signaling in accordance with anembodiment of the present invention is illustrated. As shown in FIG. 6,node (D) looses link to its current parent node (B) and accordingly thenode (D) switches its parent to new parent, node (C). Node (D) afterswitching to node (C) communicates a DAO message destined to borderrouter for record and future communication. When Node (A) which is acommon ancestor of Node (D) receives the DAO message, Node (A) detectsthat the next hop in the routing entry does not match with the next hopfrom where the DAO is received. Upon detection of such change, a NPDAOis generated by the Node (A) of behalf of Node (D) with the sequencenumber from DAO.

Referring now to FIG. 7 a DAO processing flowchart according to theconventional approach is illustrated. DAO and NPDAO messages are used inRPL to update route states for the target. Note that NPDAO is a DAOmessage with route lifetime field set to zero. A target sends a DAO toestablish routes along the path and uses NPDAO to remove the paths. Onswitching the parent node, a basic requirement for sending NPDAO is thatit should be sent along the previous path (i.e. via previous parentnode). But using previous path is inefficient because the target nodehas already switched the path because the path is either unavailable orbad (as in bad metrics). This causes inefficient NPDAO signaling.

Referring now to FIG. 8 a DAO processing flowchart in accordance with anembodiment of the present invention. According to the present invention,the target node (switching node) does not generate the NPDAO. On parentswitching the target node generates a regular DAO to establish newpaths. This regular DAO on reaching the common ancestor node, the commonancestor node detects that the DAO received is not from the same nexthop as stored in the routing entry. This becomes the basis fororiginating the NPDAO at the common ancestor node. The common ancestornode uses the PathSequence from the regular DAO message to generate theNPDAO.

As shown in FIG. 8, a switching node (node which switches the parent)sends the regular DAO to a common ancestor node. The common ancestornode is in charge of generating a No-Path DAO (NPDAO) on behalf of theswitching node.

The common ancestor receives the DAO from the switching node and finds amismatch in next hop. Mismatch is detected in the next hop in routingentry versus the next hop from which DAO is received.

The NPDAO traverses downward/downstream along the previous path, unlikeany other DAO (note that in current RPL specification, the DAO messagealways traverses upstream).

As shown in FIG. 8, the updated handling on common ancestor nodegenerates NPDAO message on behalf of the target node.

In one implementation, a corresponding pseudo-code for common ancestornode to generate NPDAO message on behalf of the target node is asfollows:

receiveDAOmessage(DAO_msg, recv_ip) {routeEntry=getRouteEntry(DAO_msg−>target); if(routeEntry == NULL) {if(DAOType == NPDAO) return; //drop message, NPDAO received but no entryin route table addRouteEntry(DAO_msg−>target, recv_ip);forwardMsg(DAO_msg, NULL); return; //Added new route entry }if(DAO_msg−>pathSeq <= routeEntry−>pathSeq) return; //drop message, oldDAO message if(DAOType == NPDAO) {invalidateRouteEntry(DAO_msg−>target); if(NPDAO is upstream) {forwardMsg(DAO_msg, NULL); return; //forwarded upstream NPDAO }fwdAddr=getNextHopAddr(DAO _(—) msg−>target); forwardDAO(DAO _(—) msg,fwdAddr); return; //forwarded downstream NPDAO } //regular DAOprocessing next_hop=getNextHopAddr(DAO_msg−>target);refreshRouteEntry(DAO_msg−>target, DAO_msg, recv_ip);forwardDAO(DAO_msg, NULL); if(next _(—) hop == recv _(—) ip) //If therouteEntry's nexthop does not change then return return; if(DAO _(—)msg−>I _(—) flag == 0) //if the I _(—) flag is not set return;//following will be invoked only on common ancestor node for regular DAOmsg generateNPDAO(type=Downstream, DAO _(—) msg−>target, DAO _(—)msg−>pathSeq); } forwardDAO(msg, fwdAddr) { if(fwdAddr == NULL) fwdAddr= getPrefParent( ); sendMsg(msg, fwdAddr); //send message on network }

The text in bold in the pseudo code above enables the generation ofdownstream NPAO message on the common ancestor node and processing ofsuch downstream NPDAO messages on intermediate routers. Note that theNPDAO signaling according to the present invention is a backwardcompatible with the previous NPDAO messaging and can work as anincremental update.

It is well known that every RPL message is divided into base messagefields and additional containers. The base fields apply to the messageas a whole and containers may be applied to specific targets. Referringto FIG. 9(a) illustrates a DAO base object as available in theprior-art.

According to the present invention, a DAO Message format is changed for:

-   -   i. Invalidate Route (I flag): The target node could decide        whether a NPDAO should be generated on its behalf by the common        ancestor node. Thus a non-target node is generating a NPDAO at        the behest of the target node. A DAO message could contain        multiple targets and this flag impact a particular target, thus        this flag has to be in context to individual target, and thus        needs to be held in the container. Either “RPL target” container        or the “Transit Information” container could be used carry this        bit. This document uses “Transit Information container” to carry        this bit.    -   ii. Reverse DAO flag (R flag): The NPDAO generated as part of        this process needs to flow downstream. Currently it is assumed        that all DAO messages including NPDAO only traverse upstream.        Thus for sending a downstream NPDAO a flag has to be added in        context to the target. This flag applies to the complete NPDAO        message and thus this flag needs to be kept at DAO base message        level and not at the container level.

Referring now to FIG. 9(b) illustrates new flags required in DAO baseobject and transit information container, in accordance with anembodiment of the present invention. As shown in the FIG. 9(b), the newflags are added in the base object and are highlighted.

Referring now to FIG. 10, use of I_flag, R_flag and Seq(PathSeq) isshown in accordance with an embodiment of the present invention. Asshown in FIG. 10, node (D) looses link to its current parent node (B)and accordingly the node (D) switches its parent to new parent, node(C). Node (D) after switching to node (C) communicates a DAO messagedestined to border router for record and future communication.Accordingly, the I_flag bit and the Seq (PathSeq) bits are set to 1 asthe parent is switched in this case; otherwise the bits are set to 0.When Node (A) which is a common ancestor of Node (D) receives the DAOmessage, Node (A) detects that the next hop in the routing entry doesnot match with the next hop from where the DAO is received. Upondetection of such change, a NPDAO is generated by the Node (A) of behalfof Node (D) with the sequence number from DAO.

According to RFC6550—the RPL specification, a PathSequence is associatedwith every target's transit information which specifies the freshness ofthe information. Every router stores this PathSequence in context to thetarget information in the routing table whenever it receives a DAO andmatches this with the incoming PathSequence in the DAO message.

The PathSequence is used as follows to decide whether to accept or dropthe DAO message:

DAO_msg->target->PathSequence<=routingEntry->PathSequence [Drop the DAOmessage]DAO_msg->target->PathSequence>routingEntry->PathSequence [Accept andprocess this DAO message]

According to the present invention, a non-target node i.e. a commonancestor generates an NPDAO on behalf of the target/switching node. Thusa choice of PathSequence becomes very important since choosing incorrectPathSequence may lead to either the NPDAO not getting honored or worstit may lead to invalidation of valid route. Also, according to thepresent invention, the common ancestor reuse the same PathSequence fromthe regular DAO based on which the NPDAO is getting generated.

In one implementation, a modified routing table structure may be asfollows:

struct_routingEntry_ { ipv6addr_t target; uint8 _(—) t pathSeq; //Lastreceived PathSequence in DAO message uint16 lifetime; struct nbrEntry*nexthop; //nexthop for routing .... }routingEntry_t;

The dependent nodes route invalidation can be handled in the same way asthe switching node. Note that there is no way that dependent nodes canset the I_flag in the DAO message since they are unaware that theirparent node is switching paths. There are two ways to handle dependentnode route invalidation:

-   -   i. One way to resolve is that the common ancestor does not        depend upon the I_flag to generate the reverse NPDAO. The only        factor it makes the decision will be based on next_hop change        for an existing target to generate the NPDAO. Thus when the        switching nodes and all the below dependent nodes advertise a        regular DAO, the common ancestor node will detect a change in        next hop and generate NPDAO for the same target as in the        regular DAO.    -   ii. Another way is that the nodes always set the I_flag whenever        they send regular DAO. Thus common ancestor will first check        whether I_flag is set and then check whether the next_hop has        changed and subsequently triggering NPDAO if required.

In one implementation, the present invention follows point 2 above. Theadvantage with I_flag is that the generation of downstream NPDAO becomesmore deterministic and the target node is still in control of its ownrouting state.

In one implementation, according to the present invention, the routeinvalidation problems mentioned in background section above do notimpact non-storing mode since no routing tables are maintained innon-storing mode on intermediate routers. Thus the I-flag and R-flagwill be unused in non-storing mode.

Conventionally, the RPL allows a node to send the same DAO throughmultiple parents, thus allowing establishment of multiple paths. Thepresent invention works transparently for this scenario.

In one implementation, I_flag is used by the target node to inform thecommon ancestor to send an NPDAO. But an implementation may choose tonot use this flag and make common ancestor decide by itself on whetherto generate NPDAO for a given target on receiving a regular DAO.

In IoT networks, such as home/building automation, Smart Meter networks,the network may form in an ad-hoc fashion. This requires multi-hop meshnetwork formation capabilities. With mesh based networks the routes aredynamically created and deleted. The process of route deletion is alsocalled route invalidation which is optimized according to the presentinvention.

Referring now to FIG. 11, an apparatus 1100 for invalidating a routingpath on switching of a parent node is disclosed. In one embodiment, theapparatus is a common ancestor node as shown in FIG. 5.

Although the present subject matter is explained considering that theapparatus 1100 is implemented as a data center, it may be understoodthat the apparatus 1100 may also be implemented in a variety ofcomputing systems, such as a laptop computer, a desktop computer, anotebook, a workstation, a mainframe computer, a server, a networkserver, and the like. It will be understood that the apparatus 1100 maybe accessed by multiple users through one or more user devices. Examplesof the user devices may include, but are not limited to, a portablecomputer, a personal digital assistant, a handheld device, and aworkstation. The apparatus 1100 is communicatively coupled to othernodes, through a network.

In one implementation, the network may be a wireless network, a wirednetwork or a combination thereof. The network can be implemented as oneof the different types of networks, such as intranet, local area network(LAN), wide area network (WAN), the internet, and the like. The networkmay either be a dedicated network or a shared network. The sharednetwork represents an association of the different types of networksthat use a variety of protocols, for example, Hypertext TransferProtocol (HTTP), Transmission Control Protocol/Internet Protocol(TCP/IP), Wireless Application Protocol (WAP), and the like, tocommunicate with one another. Further the network may include a varietyof network devices, including routers, bridges, servers, computingdevices, storage devices, and the like.

In one embodiment, the apparatus 1100 may include at least one processor1102, an input/output (I/O) interface 1104, and a memory 1106. The atleast one processor 1102 may be implemented as one or moremicroprocessors, microcomputers, microcontrollers, digital signalprocessors, central processing units, state machines, logic circuitries,and/or any devices that manipulate signals based on operationalinstructions. Among other capabilities, the at least one processor 1102is configured to fetch and execute computer-readable instructions storedin the memory 1106.

The I/O interface 1104 may include a variety of software and hardwareinterfaces, for example, a web interface, a graphical user interface,and the like. The I/O interface 1104 may allow the apparatus 1100 tointeract with a user directly or through the client devices 1104.Further, the I/O interface 1104 may enable the apparatus 1100 tocommunicate with other computing devices, such as web servers andexternal data servers (not shown). The I/O interface 1104 can facilitatemultiple communications within a wide variety of networks and protocoltypes, including wired networks, for example, LAN, cable, etc., andwireless networks, such as WLAN, cellular, or satellite. The I/Ointerface 1104 may include one or more ports for connecting a number ofdevices to one another or to another server.

The memory 1106 may include any computer-readable medium known in theart including, for example, volatile memory, such as static randomaccess memory (SRAM) and dynamic random access memory (DRAM), and/ornon-volatile memory, such as read only memory (ROM), erasableprogrammable ROM, flash memories, hard disks, optical disks, andmagnetic tapes. The memory 1106 may include logics for performingrespective functions of the apparatus 1100.

In one first embodiment, the apparatus 1100 for invalidating a routingpath on switching of a parent node includes a processor; and a memorycoupled to the processor for executing a plurality of modules present inthe memory. The plurality of modules includes a determining module 1110and a generating module 1112. The determining module 1110 is adapted todetermine switching of the parent node associated with at least one nodebased on at least one update message received from the at least one nodeusing a new routing path established on switching of the parent node.The generating module 1112 is adapted to generate at least one No-Pathmessage for invalidating the routing path associated with the at leastone node on switching of the parent node.

In one first detailed implementation of the first embodiment, theapparatus 1100 further includes a tree formation module 1114. The treeformation module 1114 adapted to represent the network by a DestinationOriented Directed Acyclic Graph (DODAG). The nodes in the graphrepresent at least the parent node, the common ancestor node, or thenode, and the common ancestor node is a root nodes root in the DODAG,and directed edges represent the links between the node, wherein the atleast one common ancestor node of the network is a node having at leasttwo nodes as descendants (the parent node and/or the nodes) in theDODAG.

In one first detailed implementation of the first embodiment, the atleast one update message is a destination oriented directed acyclicgraph advertisement object (DAO) message, and the at least one No-Pathmessage is a No-Path destination oriented directed acyclic graphadvertisement object message (NPDAO) message.

In one second detailed implementation of the first embodiment, theapparatus 1100 further includes a detecting module 1108. The detectingmodule 1108 is adapted to detect that the at least one update messagereceived from the at least one node is different from the at least oneupdate message received earlier.

In one first detailed implementation of the first embodiment, thedetermining module 1110 is further adapted to determine switching of theparent node associated with the at least one node for generating the atleast one No-Path message by utilizing a Path sequence form the at leastone update message received.

In one third detailed implementation of the first embodiment, theapparatus 1100 further includes a storage module 1116. The storagemodule 1116 is adapted to store a Path sequence associated the at leastone node before switching of the path, wherein when the at least oneupdate message received, the Path sequence form the at least one updatemessage received is compared with the pre-stored Path sequenceassociated the at least one node, and thereby generating the at leastone No-Path message.

In one fourth detailed implementation of the first embodiment, the atleast one update message received from the at least one node comprisesat least one bit, representing invalidating the routing path, placed inat least a target container or at least a transit information containeror any combination thereof, the at least one bit authorizing generationof the at least one No-Path message by the at least one common ancestornode.

In one fifth detailed implementation of the first embodiment, the atleast one No-Path message generated comprises at least one bit,representing reverse flag, adapted to traverse the No-Path messagedownstream/reverse, and placed in a base message level of the No-Pathmessage.

In one second embodiment, the apparatus 1100 for invalidating a routingpath on switching of a parent node in a network is disclosed. Thenetwork is represented by a Destination Oriented Directed Acyclic Graph(DODAG), the nodes in the graph represent at least the parent node, atleast a common ancestor node, or at least a node, and the commonancestor node is a root nodes root in the DODAG, and directed edgesrepresent the links between the node for routing packets between thenodes. The apparatus 1100 includes a determining module 1110 and agenerating module 1112. The determining module 1110 adapted to determineswitching of the parent node associated with the at least one node basedon at least one a destination oriented directed acyclic graphadvertisement object (DAO) message received from the at least one nodeusing a new routing path established on switching of the parent node.The generating module 1112 adapted to generate at least one No-Pathdestination oriented directed acyclic graph advertisement object message(NPDAO) message for invalidating the routing path associated with the atleast one node on switching of the parent node.

In one first detailed implementation of the second embodiment, theapparatus 1100 further includes an interface 1104 adapted to receive theDAO message from the at least one node. The determining module 1110 uponreceiving the DAO message is further adapted to determine a mismatch ina next hop of a routing entry associated with a Path sequence pre-storedagainst a next hop of a routing entry associated with a Path sequence ofthe DAO message received. The generating module 1112 is further adaptedto generate at least one No-Path destination oriented directed acyclicgraph advertisement object message (NPDAO) message for invalidating therouting path associated with the at least one node on switching of theparent node.

In one second detailed implementation of the second embodiment, therouting uses a Routing Protocol for Low Power and Lossy Networks (RPL).

In one second detailed implementation of the second embodiment, theNPDAO message traverses downward/downstream along the Path sequence ofthe DAO message received.

In one second detailed implementation of the second embodiment, the atleast one update message received from the at least one node comprisesat least one bit, representing invalidating the routing path, placed inat least a target container or at least a transit information containeror any combination thereof, the at least one bit authorizing generationof the at least one No-Path message by the at least one common ancestornode.

In one second detailed implementation of the second embodiment, the atleast one No-Path message generated comprises at least one bit,representing reverse flag, adapted to traverse the No-Path messagedownstream/reverse, and placed in a base message level of the No-Pathmessage.

In one third detailed implementation of the second embodiment, theapparatus 1100 further includes a utilizing module adapted to utilizethe Path sequence from the at least one DAO message to generate theNPDAO message.

Referring to FIG. 12, a method for invalidating a routing path onswitching of a parent node is illustrated, in accordance with anembodiment of the present subject matter. The method may be described inthe general context of computer executable instructions. Generally,computer executable instructions can include routines, programs,objects, components, data structures, procedures, modules, functions,etc., that perform particular functions or implement particular abstractdata types. The method may also be practiced in a distributed computingenvironment where functions are performed by remote processing devicesthat are linked through a communications network. In a distributedcomputing environment, computer executable instructions may be locatedin both local and remote computer storage media, including memorystorage devices.

The order in which the method is described is not intended to beconstrued as a limitation, and any number of the described method blockscan be combined in any order to implement the method or alternatemethods. Additionally, individual blocks may be deleted from the methodwithout departing from the protection scope of the subject matterdescribed herein. Furthermore, the method can be implemented in anysuitable hardware, software, firmware, or combination thereof. However,for ease of explanation, in the embodiments described below, the methodmay be considered to be implemented in the above described apparatus1100.

Referring now to FIG. 12, at step 1202 a common ancestor node/apparatus1100 receives a DOA message form a switching node in the network.

At step 1204, common ancestor node/apparatus 1100 receives a DAO for atarget and finds a mismatch in next hop. Mismatch is detected in thenext hop in routing entry versus the next hop from which DAO isreceived.

At step 1206, using the changed signaling, the common ancestor nodegenerates an NPDAO on behalf of the target node on receiving a refreshedDAO from an alternate path. The common ancestor node is in charge ofgenerating a No-Path DAO on behalf of the switching node.

In one embodiment, the method for invalidating a routing path onswitching of a parent node, includes determining, by at least one commonancestor node of a network, switching of the parent node associated withat least one node based on at least one update message received from theat least one node using a new routing path established on switching ofthe parent node; and generating, by the at least one common ancestornode, at least one No-Path message for invalidating the routing pathassociated with the at least one node on switching of the parent node.

In one embodiment, the method for invalidating a routing path onswitching of a parent node in a network is disclosed. The network isrepresented by a Destination Oriented Directed Acyclic Graph (DODAG),the nodes in the graph represent at least the parent node, at least acommon ancestor node, or at least a node, and the common ancestor nodeis a root nodes root in the DODAG, and directed edges represent thelinks between the node for routing packets between the nodes. The methodincludes determining, by the at least one common ancestor node of thenetwork, switching of the parent node associated with the at least onenode based on at least one a destination oriented directed acyclic graphadvertisement object (DAO) message received from the at least one nodeusing a new routing path established on switching of the parent node;and generating, by the at least one common ancestor node, at least oneNo-Path destination oriented directed acyclic graph advertisement objectmessage (NPDAO) message for invalidating the routing path associatedwith the at least one node on switching of the parent node.

Application Scenarios

Smart Meter Scenario: Thousands of smart meters interconnect via eachother to form a mesh network. The upstream nodes usually take a higherload since the entire downstream nodes route through them. If routeinvalidation does not work optimally then upstream nodes suffer becausein case of contention i.e. in case they receive route add request and ifthe route table is full then evicting the stale entry is difficult sincethe route invalidation does not function optimally. The implementationof the present invention in the network improves the route invalidationoperation significantly and thus improves route table usage efficiency.

General IoT Solutions: Any wireless/wired IoT or MANET (Mobile Ad-hocnetwork) solution which uses multi-hop mesh based network formation willbenefit from the present invention. This includes but not limited toHome automation, Smart city solution based on BLE (Bluetooth LowEnergy), LoWPAN/802.15.4, or adhoc WiFi.

Apart from what is discussed above, the present invention also includessome additional technical benefits, few of them are mentioned below:

-   -   i. Routing table reflects latest state of network topology.    -   ii. Improved memory utilization: Improves route invalidation and        thus improves resource utilization on constrained nodes. In        earlier case, a nodes routing table could become bloated because        of stale route entries. By implementing the present invention,        because of efficient route invalidation, the stale route entries        are minimized.    -   iii. Reduced control traffic: NPDAO signaling path is        significantly reduced. In earlier case, an NPDAO traversed a        complete path from the target node to all the way till border        router. By implementing the present invention, the NPDAO path is        limited between common ancestor nodes to the switching node's        previous preferred parent.    -   iv. Dependent Node route invalidation: Current RPL specification        does not cater to dependent nodes route invalidation altogether.        By implementing the present invention, route invalidation works        for dependent nodes as well.    -   v. P2P traffic: Improved efficiency of P2P traffic, by reducing        downtime caused due to invalid route entries.    -   vi. Reduced route downtime: The present invention results in        synchronous operation of regular DAO and NPDAO thus reducing        possibility of route downtime.    -   vii. The present invention provides a new signaling mechanism        for route invalidation in constrained networks.    -   viii. The present invention enables generation of NPDAO by a        common ancestor node rather than the target node itself. As per        this claim, the NPDAO on behalf of the target node is generated        by common ancestor node.    -   ix. The present invention enables downstream signaling of NPDAO        as compared to upstream signaling as per the current standard.    -   x. The present invention enables common ancestor node to detect        routing anomaly using next hop mismatch on reception of regular        DAO to generate NPDAO on behalf of the target node    -   xi. The present invention enables the common ancestor node to        reuse the state information of regular DAO to generate NPDAO.        One of the primary parameters of this state information is the        PathSequence number.    -   xii. The present invention enables node sends parent information        in DAO message which gets stored in routing table along with        other information.    -   xiii. According to the present invention, same common ancestor        node is in charge of generating a downstream/reverse NPDAO for        the switching node and all the dependent nodes, the aggregation        of such NPDAO messages becomes computationally efficient and        less complex in terms of program memory.    -   xiv. The present invention enables synchronous operation of DAO        and NPDAO i.e. generation of NPDAO in response to a regular DAO        at common ancestor results in reduced route downtime

It may be understood by the person skilled in the art that though thepresent invention is discussed in context to Low power and lossynetworks but it can also be used in context to Mobile Ad-hoc networks(MANET) or any other ad-hoc/mesh based topology formation scenario.

It may be understood by the person skilled in the art that any routingprotocol is based on similar semantics. Thus the present invention maybe used in conjunction with routing protocol for improved routeinvalidation.

It may be understood by the person skilled in the art that though thepresent invention uses RPL as an example to discuss about networkformation. But essentially any proactive routing protocol which supportsrouting metrics/constraints can be used. Other examples of proactiverouting protocols are BABEL, RIP etc.

It may be understood by the person skilled in the art that the DAOmessages can be aggregated i.e. multiple DAO messages can be clubbedinto single message and then transmitted to reduce network trafficoverhead. The idea should work transparently with aggregated messages aswell.

A person skilled in the art may understand that any known or newalgorithms by be used for the implementation of the present invention.However, it is to be noted that, the present invention provides a methodto be used during back up operation to achieve the above mentionedbenefits and technical advancement irrespective of using any known ornew algorithms.

A person of ordinary skill in the art may be aware that in combinationwith the examples described in the embodiments disclosed in thisspecification, units and algorithm steps may be implemented byelectronic hardware, or a combination of computer software andelectronic hardware. Whether the functions are performed by hardware orsoftware depends on the particular applications and design constraintconditions of the technical solution. A person skilled in the art mayuse different methods to implement the described functions for eachparticular application, but it should not be considered that theimplementation goes beyond the scope of the present invention.

It may be clearly understood by a person skilled in the art that for thepurpose of convenient and brief description, for a detailed workingprocess of the foregoing system, apparatus, and unit, reference may bemade to a corresponding process in the foregoing method embodiments, anddetails are not described herein again.

In the several embodiments provided in the present application, itshould be understood that the disclosed system, apparatus, and methodmay be implemented in other manners. For example, the describedapparatus embodiment is merely exemplary. For example, the unit divisionis merely logical function division and may be other division in actualimplementation. For example, a plurality of units or components may becombined or integrated into another system, or some features may beignored or not performed. In addition, the displayed or discussed mutualcouplings or direct couplings or communication connections may beimplemented through some interfaces. The indirect couplings orcommunication connections between the apparatuses or units may beimplemented in electronic, mechanical, or other forms.

When the functions are implemented in a form of a software functionalunit and sold or used as an independent product, the functions may bestored in a computer-readable storage medium. Based on such anunderstanding, the technical solutions of the present inventionessentially, or the part contributing to the prior art, or a part of thetechnical solutions may be implemented in a form of a software product.The computer software product is stored in a storage medium, andincludes several instructions for instructing a computer node (which maybe a personal computer, a server, or a network node) to perform all or apart of the steps of the methods described in the embodiment of thepresent invention. The foregoing storage medium includes: any mediumthat can store program code, such as a USB flash drive, a removable harddisk, a read-only memory (Read-Only Memory, ROM), a random access memory(Random Access Memory, RAM), a magnetic disk, or an optical disc.

Devices that are in communication with each other need not be incontinuous communication with each other, unless expressly specifiedotherwise. In addition, devices that are in communication with eachother may communicate directly or indirectly through one or moreintermediaries.

When a single device or article is described herein, it will be readilyapparent that more than one device/article (whether or not theycooperate) may be used in place of a single device/article. Similarly,where more than one device or article is described herein (whether ornot they cooperate), it will be readily apparent that a singledevice/article may be used in place of the more than one device orarticle or a different number of devices/articles may be used instead ofthe shown number of devices or programs. The functionality and/or thefeatures of a device may be alternatively embodied by one or more otherdevices which are not explicitly described as having suchfunctionality/features. Thus, other embodiments of the invention neednot include the device itself.

Finally, the language used in the specification has been principallyselected for readability and instructional purposes, and it may not havebeen selected to delineate or circumscribe the inventive subject matter.It is therefore intended that the scope of the invention be limited notby this detailed description, but rather by any claims that issue on anapplication based here on. Accordingly, the disclosure of theembodiments of the invention is intended to be illustrative, but notlimiting, of the scope of the invention, which is set forth in thefollowing claims.

With respect to the use of substantially any plural and/or singularterms herein, those having skill in the art can translate from theplural to the singular and/or from the singular to the plural as isappropriate to the context and/or application. The varioussingular/plural permutations may be expressly set forth herein for sakeof clarity.

Although implementations for apparatus and method for optimized routeinvalidation using modified no-path DAO signaling have been described inlanguage specific to structural features and/or methods, it is to beunderstood that the appended claims are not necessarily limited to thespecific features or methods described. Rather, the specific featuresand methods are disclosed as examples of implementations of apparatusand method for optimized route invalidation using modified no-path DAOsignaling.

We claim:
 1. A method for invalidating a routing path on switching of aparent node, the method comprising: determining, by at least one commonancestor node of a network, switching of the parent node associated withat least one node based on at least one update message received from theat least one node using a new routing path established on switching ofthe parent node; generating, by the at least one common ancestor node,at least one No-Path message for invalidating the routing pathassociated with the at least one node on switching of the parent node.2. The method as claimed in claim 1, further comprises: representing thenetwork by a Destination Oriented Directed Acyclic Graph (DODAG),wherein nodes in the graph represent at least the parent node, thecommon ancestor node, or the node, and the common ancestor node is anupstream node common on both the paths (the new path and the previouspath) in the DODAG, and directed edges represent the links between thenode, wherein the at least one common ancestor node of the network is anode having at least two nodes as descendants (the parent node and/orthe nodes) in the DODAG.
 3. The method as claimed in claim 1, whereinthe routing path associated with the at least one node is a pathestablished for communication before switching of the parent node. 4.The method as claimed in claim 1, wherein the at least one updatemessage is received from the at least one node while establishing newpaths in the network upon switching of the parent node.
 5. The method asclaimed in claim 1, wherein the at least one node and the at least onecommon ancestor node are communicably coupled.
 6. The method as claimedin claim 1, wherein the at least one update message is a destinationoriented directed acyclic graph advertisement object (DAO) message. 7.The method as claimed in claim 1, wherein the at least one No-Pathmessage is a No-Path destination oriented directed acyclic graphadvertisement object message (NPDAO) message.
 8. The method as claimedin claim 1, wherein the at least one common ancestor node determinesswitching of the parent node associated with the at least one node forgenerating the at least one No-Path message by: detecting that the atleast one update message received from the at least one node haschanged.
 9. The method as claimed in claim 1, wherein the at least onecommon ancestor node determines switching of the parent node associatedwith the at least one node for generating the at least one No-Pathmessage by utilizing a path sequence from the at least one updatemessage received.
 10. The method as claimed in claim 1, wherein the atleast one common ancestor node comprises a pre-stored Path sequenceassociated the at least one node before switching of the path, when theat least one update message received, the Path sequence form the atleast one update message received is compared with the pre-stored pathsequence associated the at least one node, and thereby generating the atleast one No-Path message.
 11. The method as claimed in claim 1, whereinthe at least one update message received from the at least one nodecomprises at least one bit, representing invalidating the routing path,placed in at least a target container or at least a transit informationcontainer or any combination thereof, the at least one bit authorizinggeneration of the at least one No-Path message by the at least onecommon ancestor node.
 12. The method as claimed in claim 1, wherein theat least one No-Path message generated comprises at least one bit,representing reverse flag, adapted to traverse the No-Path messagedownstream/reverse, and placed in a base message level of the No-Pathmessage.
 13. A method for invalidating a routing path on switching of aparent node in a network, wherein the network is represented by aDestination Oriented Directed Acyclic Graph (DODAG), the nodes in thegraph represent at least the parent node, at least a common ancestornode, or at least a node, and the common ancestor node is an upstreamnode common on both the paths (the new path and the previous path) inthe DODAG, and directed edges represent the links between the node forrouting packets between the nodes, the method comprising: determining,by the at least one common ancestor node of the network, switching ofthe parent node associated with the at least one node based on at leastone a destination oriented directed acyclic graph advertisement object(DAO) message received from the at least one node using a new routingpath established on switching of the parent node; generating, by the atleast one common ancestor node, at least one No-Path destinationoriented directed acyclic graph advertisement object message (NPDAO)message for invalidating the routing path associated with the at leastone node on switching of the parent node.
 14. The method as claimed inclaim 13, wherein the routing uses a Routing Protocol for Low Power andLossy Networks (RPL).
 15. The method as claimed in claim 13, furthercomprises: receiving, by the at least one common ancestor node of thenetwork, the DAO message from the at least one node; determining amismatch in a next hop of a routing entry associated with a targetand/or Path sequence pre-stored against a next hop of a routing entryassociated with a target and/or Path sequence of the DAO messagereceived; and thereby generating, by the at least one common ancestornode, the at least one No-Path destination oriented directed acyclicgraph advertisement object message (NPDAO) message for invalidating therouting path associated with the at least one node on switching of theparent node.
 16. The method as claimed in claim 13, wherein the NPDAOmessage traverses downward/downstream along the Path sequence of the DAOmessage received.
 17. The method as claimed in claim 13, wherein the atleast one DAO message is generated by the at least one node to establishnew paths on switching of the parent node.
 18. The method as claimed inclaim 13 further comprises: utilizing the Path sequence from the atleast one DAO message to generate the NPDAO message.
 19. The method asclaimed in claim 13, wherein the at least one update message receivedfrom the at least one node comprises at least one bit, representinginvalidating the routing path, placed in at least a target container orat least a transit information container or any combination thereof, theat least one bit authorizing generation of the at least one No-Pathmessage by the at least one common ancestor node.
 20. The method asclaimed in claim 13, wherein the at least one No-Path message generatedcomprises at least one bit, representing reverse flag, adapted totraverse the No-Path message downstream/reverse, and placed in a basemessage level of the No-Path message.
 21. An apparatus for invalidatinga routing path on switching of a parent node, the apparatus comprising:a processor; a memory coupled to the processor for executing a pluralityof modules present in the memory, the plurality of modules comprising: adetermining module adapted to determine switching of the parent nodeassociated with at least one node based on at least one update messagereceived from the at least one node using a new routing path establishedon switching of the parent node; a generating module adapted to generateat least one No-Path message for invalidating the routing pathassociated with the at least one node on switching of the parent node.22. The apparatus as claimed in claim 21, further comprises: a treeformation module adapted to represent the network by a DestinationOriented Directed Acyclic Graph (DODAG), wherein nodes in the graphrepresent at least the parent node, the common ancestor node, or thenode, and the common ancestor node is a root nodes root in the DODAG,and directed edges represent the links between the node, wherein the atleast one common ancestor node of the network is a node having at leasttwo nodes as descendants (the parent node and/or the nodes) in theDODAG.
 23. The apparatus as claimed in claim 21, wherein the at leastone update message is a destination oriented directed acyclic graphadvertisement object (DAO) message, and the at least one No-Path messageis a No-Path destination oriented directed acyclic graph advertisementobject message (NPDAO) message.
 24. The apparatus as claimed in claim 21further comprises: a detecting module adapted to detect that the atleast one update message received from the at least one node haschanged.
 25. The apparatus as claimed in claim 21, wherein thedetermining module is further adapted to determine switching of theparent node associated with the at least one node for generating the atleast one No-Path message by utilizing a Path sequence form the at leastone update message received.
 26. The apparatus as claimed in claim 21further comprises a storage module adapted to store a Path sequenceassociated the at least one node before switching of the path, whereinwhen the at least one update message received, the Path sequence formthe at least one update message received is compared with the pre-storedPath sequence associated the at least one node, and thereby generatingthe at least one No-Path message.
 27. The apparatus as claimed in claim21, wherein the at least one update message received from the at leastone node comprises at least one bit, representing invalidating therouting path, placed in at least a target container or at least atransit information container or any combination thereof, the at leastone bit authorizing generation of the at least one No-Path message bythe at least one common ancestor node.
 28. The apparatus as claimed inclaim 21, wherein the at least one No-Path message generated comprisesat least one bit, representing reverse flag, adapted to traverse theNo-Path message downstream/reverse, and placed in a base message levelof the No-Path message.
 29. An apparatus for invalidating a routing pathon switching of a parent node in a network, wherein the network isrepresented by a Destination Oriented Directed Acyclic Graph (DODAG),the nodes in the graph represent at least the parent node, at least acommon ancestor node, or at least a node, and the common ancestor nodeis a root nodes root in the DODAG, and directed edges represent thelinks between the node for routing packets between the nodes, theapparatus comprising: a processor; a memory coupled to the processor forexecuting a plurality of modules present in the memory, the plurality ofmodules comprising: a determining module adapted to determine switchingof the parent node associated with the at least one node based on atleast one a destination oriented directed acyclic graph advertisementobject (DAO) message received from the at least one node using a newrouting path established on switching of the parent node; a generatingmodule adapted to generate at least one No-Path destination orienteddirected acyclic graph advertisement object message (NPDAO) message forinvalidating the routing path associated with the at least one node onswitching of the parent node.
 30. The apparatus as claimed in claim 29,wherein the routing uses a Routing Protocol for Low Power and LossyNetworks (RPL).
 31. The apparatus as claimed in claim 29, furthercomprises: an interface adapted to receive the DAO message from the atleast one node; the determining module further adapted to determine amismatch in a next hop of a routing entry associated with a Pathsequence pre-stored against a next hop of a routing entry associatedwith a Path sequence of the DAO message received; and the generatingmodule further adapted to generate at least one No-Path destinationoriented directed acyclic graph advertisement object message (NPDAO)message for invalidating the routing path associated with the at leastone node on switching of the parent node.
 32. The apparatus as claimedin claim 29, wherein the NPDAO message traverses downward/downstreamalong the Path sequence of the DAO message received.
 33. The apparatusas claimed in claim 29 further comprises: a utilizing module adapted toutilize the Path sequence from the at least one DAO message to generatethe NPDAO message.
 34. The apparatus as claimed in claim 29, wherein theat least one update message received from the at least one nodecomprises at least one bit, representing invalidating the routing path,placed in at least a target container or at least a transit informationcontainer or any combination thereof, the at least one bit authorizinggeneration of the at least one No-Path message by the at least onecommon ancestor node.
 35. The apparatus as claimed in claim 29, whereinthe at least one No-Path message generated comprises at least one bit,representing reverse flag, adapted to traverse the No-Path messagedownstream/reverse, and placed in a base message level of the No-Pathmessage.